This invention relates to an overhead-valve, horizontal-shaft, general-purpose internal combustion engine, and more particularly to the arrangement and construction of a compact engine of this type which is particularly useful for mounting on a cultivator or a portable electric generator.
Conventionally, a side valve (SV) engine has been exclusively used where a compact, horizontal-shaft, general-purpose engine is required for a cultivator or a generator, for example. This engine design is used because the overall contour of the engine is compact and generally cubic so that it is suitable for mounting on cultivators or other various types of work equipment, because the construction of the engine itself is not complicated, and also because the cost of production is low.
Such a horizontal-shaft general-purpose SV engine is generally constructed to adapt to one of two types of systems. In one of the two systems, a power output shaft extends directly from the crankshaft. In the other system, a power output shaft extends from the camshaft and has a rotational speed about one-half that of the crankshaft, and this engine is used in applications where relatively low speeds are needed.
In recent years, in lieu of side valve engines as described above, overhead valve (OHV) engines have gained popularity due to their higher burning efficiency, larger horsepower per unit displacement, lower vibration levels, and other advantages.
In the OHV engine, however, because the valves are located in the upper portion of the engine cylinder, the conventional engine has a higher vertical dimension than an SV engine. The conventional way to mount a general-purpose OHV engine in a specified height has been, as shown in FIG. 3, to incline the axis of the cylinder 1 at about 55-65 degrees. As shown in FIG. 4, the conventional OHV engine has a carburetor 9 located on the side of the upper portion of the inclined cylinder, which is on the side opposite the output shaft 2, and has an air cleaner 10 provided through and above an L-shape air-inlet pipe 13. A fuel tank 11 is mounted above the crankcase 4 (see FIG. 3), and the fuel is fed by gravity flow through a fuel pipe (not shown) to the carburetor 9.
In the arrangement and construction of the above-mentioned horizontal-shaft, compact general-purpose OHV engine, it is impossible to establish a large engine head between the fuel tank and the carburetor. For this reason, this gravity type fuel feed, compact, general-purpose engine suffers from its inability to be used when the entire engine is in an inclined position during operation. The power output shaft extending from the camshaft 3 (FIG. 3) is so close to the engine mount base, that a large-diameter pulley cannot be mounted on the output shaft side in a camshaft speed-reducing engine. If the camshaft driving gear 3' is immersed in the engine oil in the crankcase, the oil agitation causes oil temperature buildup. Thus, the oil level must be lowered according to the position of the camshaft 3, making it difficult to reserve a sufficient amount of oil. As described hereinabove, in such a construction where the carburetor 9 is located on a side of the upper portion of the cylinder 1, the end face of the carburetor 9 which connects with the air cleaner 10 projects almost up to the end face of the fan cover 16. Accordingly, it is necessary to connect the carburetor 9 with the air cleaner 10, which is located above the carburetor 9, indirectly through the L-shaped inlet pipe 13 or the like, resulting in a more complicated construction and a lower breathing efficiency. Furthermore, unused or dead space D is created below the cylinder 1, which makes the external dimensions of the entire engine larger.
It is a general object of this invention to provide a horizontal-shaft, compact, general-purpose OHV engine which overcomes the foregoing problems and has compact external dimensions per engine displacement.